Sealing and bearing arrangement in electrical toothbrushes

ABSTRACT

A sealing and bearing arrangement in electric toothbrushes is characterized by a sealing ring (9) for preventing foreign material from penetrating into a bearing space, the ring being arranged around a nose pin (1) in the open end (7) of a casing (5), which coaxially surrounds the nose pin (1), and being immobile when the nose pin (1) rotates; an annular supporting plate (10) which is provided close to and inwardly of the sealing ring (9) and which is immobile when the nose pin (1) rotates; and bearing balls (11) provided in two races, one on each side of a thickened portion (4) of the central member of the nose pin (1), for taking up forces in all directions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sealing and bearing arrangement inelectric toothbrushes comprising a cylindrical, rotatable nose pin whichhas a front member on which the brush is to be mounted, a rear memberwith a means transmitting power from a motor, and a central memberpartly consisting of a thickened portion; and a hollow casing which isimmobile when the nose pin rotates and which coaxially encompasses thecentral member, including said thickened portion, and whose front end isopen, while its rear end sealingly ecompasses the nose pin, there beinga clearance between the inner surface of the casing and the centralmember of the nose pin.

2. Description of the Prior Art

Electric toothbrushes have been on the market for many years, and aplurality of differently functioning designs have gradually beendeveloped. However, many of these are disadvantageous in one respect orthe other, e.g. by having too short a service life.

A usual incovenience is that the front member, on which the brush forbrushing the teeth and the gums is mounted, is not sufficiently sealedoff. Thus, foreign unwanted material, e.g. water, saliva, blood, andtoothpaste ingredients, such as pumice, may penetrate into and damagethe interior of the toothbrush.

Present-day electric toothbrushes with rotating brushing action comprisea casing which coaxially encompasses a central thickened portion of arotatable nose pin which drives and rotates the brush. Between the innersurface of the casing and the outer surface of the thickened portion,there is a slide bearing space containing a lubricant. A rubber O-ringis provided in the front end of the casing to prevent foreign materialfrom penetrating into the slide bearing space. However, the sealingaction of the O-ring is inadequate. When foreign material penetratesinto the slide bearing space, the friction increases, resulting in thatheat is generated, the lubricant dries, and wear arises. The toothbrushsimply functions so badly that it stalls from time to time and finallystops working at all. Furthermore, lubricant may escape in bothdirections from the leaky bearing space, and the loss of lubricant mayalso cause the above-mentioned inconveniences.

Another inconvenience is that the bearing of the toothbrush is notsufficiently strong to withstand the severe, differently directed loadsto which it is subjected during teeth brushing. Adjacent to the rearedge of the thickened portion, an annular collar is provided around thenose pin to serve as a hold-up means for the casing and to take up axialforces. The collar is maintained in place by an annular bronze platearranged around the nose pin, adjacent to the rear edge of the collar.The contact between the collar and the casing has a certain brakingeffect with ensuing wear. Also, the friction between the mutuallyadjacent surfaces of the collar and the bronze plate contributes to thisbraking effect and ensuing wear. The wear also entails a disagreeablesqueaking noise and gradually impairs the function of the bearing.

Consequently, there is need for an electric toothbrush with rotatingbrushing action, which is sealed against unwanted materials and which ismounted in bearings adapted to take up considerable forces in alldirections.

SUMMARY OF THE INVENTION

The object of the present invention is to obviate the aboveinconveniences by providing an improved electric toothbrush.

This object is achieved by means of the combined sealing and bearingarrangement according to the invention, which shows the distinctivefeatures stated in the appended claims.

The combined sealing and bearing arrangement according to the inventiongives an electric toothbrush which is more durable and affords a muchhigher sealing action than known electric toothbrushes. The inventivebearing arrangement can withstand heavier loads, which makes it possibleto clean the teeth and the gums more efficiently. Furthermore, it allowsa larger space for the lubricant and, consequently, a larger amount oflubricant for the bearing, thus improving the function and sealingfactor thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, reference being hasto the accompanying drawings, in which

FIG. 1 illustrates the sealing and bearing arrangement according to theinvention, as it is adapted to be enclosed in the front member of anelectric toothbrush and

FIG. 2 is a diagram illustrating the load as a function of time in aload endurance test carried out with four different toothbrushes.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

As shown in FIG. 1, a cylindrical, rotatable nose pin 1 has a frontmember 2 on which the brush 12 is mounted, a rear member 3 connected,via a power-transmitting means 14, to a motor 3A, and a central memberpartly consisting of a thickened portion 4. Between the thickenedportion 4 and the rear member 3, the diameter of the nose pin 1 isreduced by steps, as shown in the drawing. A hollow casing 5, which isimmobile when the nose pin 1 rotates, coaxially encompasses the centralmember, including the thickened portion 4 of the nose pin 1. The frontend 7 of the casing 5 is open, while its rear end 8 closely surroundsthe nose pin 1. Between the inner surface of the casing 5 and thethickened portion 4, there is a clearance 6 adapted to accommodatelubricant. A sealing ring 9 is arranged around the nose pin 1 in thefront end 7 of the casing 5. An annular supporting plate 10 is providedaround the nose pin 1, close to and inwardly of the sealing ring 9.Bearing balls 11 are provided in two annular races located one on eachside of the thickened portion 4. The front race is defined by thesupporting plate 10, the inner surface of the casing 5, the nose pin 1and the front edge of the thickened portion 4, while the rear race isdefined by the rear end 8 of the casing 5, the inner surface of thecasing 5, the nose pin 1 and the rear edge of the thickened portion 4.By this combination, there is achieved a thrust bearing which takes upforces in all directions.

The sealing ring 9, which preferably is made of PTFE-Teflon®, is appliedto the nose pin 1, which preferably is made of stainless steel, in apress fit. Since the inner diameter of the sealing ring 9 is smallerthan the diameter of the nose pin 1, a so-called lip ring is obtained onwhich an annular ridge (not shown in FIG. 1) is formed on the front ofthe sealing ring 9 against the surface of the nose pin 1. The lip ringprevents undesired and foreign material from penetrating into theinterior of the toothbrush. Both the supporting plate 10, whichpreferably is made of steel, and the sealing ring 9 are mounted in apress fit in the open front end 7 of the casing 5. Since the innerdiameter of the supporting plate 10 exceeds the diameter of the nose pin1, the supporting plate 10 does not rotate when the nose pin 1 rotates,and also the sealing ring 9 is at standstill when the nose pin 1rotates, since the friction between the outer circumferential edgesurface of the sealing ring 9 and the inner circumferential surface ofthe casing 5, which preferably is made of steel, is higher than thatbetween the inner circumferential surface of the sealing ring 9 and theouter circumferential surface of the nose pin 1. The supporting plate 10is maintained in place between the sealing ring 9 and an edge of theinside of the casing 5, as is apparent from FIG. 1. The supporting plate10 serves as support and abutment for the bearing balls 11, whichpreferably are made of hardened steel. If the bearing balls 11 had beendirectly applied against the sealing ring 9 of Teflon®, the axial thrustaction during operation of the toothbrush would have caused recesses toform in the softer sealing ring 9 with ensuing wear. The ball bearings11 also serve to prevent lubricant from excaping at the two ends of thegap 6.

The entire sealing and bearing arrangement, including the casing, issealingly accommodated in a space of the same shape as the plastic cover13 accommodating the entire toothbrush. The outer surface of the casing5 is formed with slits in the axial direction, and the inside of thecover is provided with ridges extending in the circumferentialdirection. Thus, no foreign material can penetrate between the outersurface of the casing 5 and the inner surface of the cover and,consequently, neither can any such material penetrate into the interiorof the casing 5 from the rear end portion thereof.

The type of watertight bearings with small bearing balls provided by thepresent invention is not available in the market but is altogetherunique. Moreover, a press fit seal is not previously known in thiscontext. At the tests described below, this seal has proved to be veryefficient, and no trace of any foreign material has been found in thebearing space. In these tests, which were executed at different loads,the bearing device according to the invention proved to be much moredurable than other types of bearings, and its durability was,furthermore, found to increase after a running-in period.

In a preferred embodiment of the invention, thirteen steel balls 11 witha diameter of 0.8 mm are arranged in each of the two races. Lubricantfor the bearing is accommodated in these races and in the clearance 6between the inner surface of the casing 5 and the central member,including the thickened portion 4 of the nose pin 1. Furthermore, theouter diameter of the sealing ring 9 is 4.5 mm, the inner diameter is2.5 mm, and the height is 0.8 mm. The outer diameter of the supportingplate 10 is 4.5 mm, the inner diameter is 2.7 mm, and the height is 0.25mm. The outer diameter of the casing 5 is 5.3 mm, and the inner diameteris 4.2 mm. The diameter of the nose pin 1 is 2.6 mm, the diameter of thethickened portion 4 is 3.8 mm, and the diameter of the thinner portionof the nose pin 1 closest to the rear member 3 is 2.0 mm.

At the rear member 3 of the nose pin 1, a powertransmitting means, e.g.in the form of an S-hook, a gear wheel, or a single or double universaljoint, is connected to the motor adapted to rotate the nose pin 1 andusually disposed in the rear end of the toothbrush.

The tests described below concern the sealing ability and load enduranceof toothbrushes equipped with the sealing and bearing arrangementaccording to the invention.

Sealing Test

In a sealing test of an electric toothbrush with the sealing and bearingarrangement according to the invention, the toothbrush was subjected tothrust load at different angles when resting on a horizontal, stationarypair of scales indicating the size of the load. After the toothbrush hadbeen subjected to load for a given period of time, the sealing andbearing arrangement was tested for watertightness. The brush was placedin an upright position, a hose with an inner diameter of 8.0 mm and anouter diameter of 12.5 mm was mounted vertically on the tip of thetoothbrush and filled with a water column about 20 cm high, the waterlevel in the hose was carefully read after a given period of time, andthe hose and the water column were removed.

The procedure below was used for a more accurate test of thewatertightness of the inventive toothbrush. First, the toothbrush wassubjected to load and was rotated for 2 min. at an angle of 45° to thesupporting surface. This may be regarded as corresponding to thebrushing of molars. Then, the toothbrush was connected to the abovewater column for 2 min., and the subsequent careful reading of theheight of the water column showed that the sealing arrangement accordingto the invention holds absolutely thight. This test was repeated anotherfour times in succession.

Then, the toothbrush was subjected to load at 45° to the supportingsurface and stopped at a load of 1500 g. Subsequently, the brush wasloaded axially and stopped at a load of 8000 g. After being connectedwith water as above for 2 min., the toothbrush proved to be watertight.After that, the toothbrush was in unloaded operation for 60 min., andafter being connected with water for 2 min., it proved to be watertight.Then, the toothbrush was recharged for 20 h. After that, it wassubjected to load (it stopped at 100 g) at 45°, connected with water for2 min. (watertightness was established), again loaded at 45° (it stoppedat 1800 g), and connected with water for 3 min. (watertightness wasestablished).

Then, the toothbrush was subjected 13 times in succession to load at 45°and connected with water for 3 min. after each time and stopped at loadsbetween 1900 and 2400 g. Each time, the brush proved to be watertight.After that, the brush was subjected 5 times in succession to load for 3min., the brush being rotated all the time at an angle of 45° to thesupporting surface, whereupon it was connected with water for 3 min. andeach time proved to be watertight. Finally, the clearance 6 between thecasing 5 and thickened portion 4 was viewed through a microscope, but noleak could be found, for which reason a toothbrush equipped with thesealing and bearing arrangement according to the invention must beregarded as extremely watertight.

Load Endurance Test

Four different toothbrushes equipped with different bearing devices weretested as to their ability to withstand load. Toothbrush A correspondsto the prior art toothbrush described above. Toothbrush B is similar totoothbrush A, but has no collar or bronze plate. Toothbrush C is similarto toothbrush B, but its thickened portion is longer in the axialdirection, and there are also some differences in the design of the gearwheels in the transmission mechanism of the toothbrush. Toothbrush D isequipped with the sealing and bearing arrangement according to theinvention.

In the tests, each brush was subjected to load at 45° to a horizontal,stationary supporting surface in the form of a pair of scales. Thus, theload (in grammes) at which the toothbrush stopped could be read andmarked in the diagram shown in FIG. 2. Then, each toothbrush was inunloaded operation for 4 min., whereupon another load endurance test wascarried out. These tests were repeated at 4-minute intervals for 84 min.The results are shown in the diagram in FIG. 2. The asterisks withinparentheses (toothbrush D) indicates that the brush proper had been wornout, necessitating the mounting of a new brush for the subsequent test.

These results prove that toothbrush D equipped with the sealing andbearing arrangement according to the invention can withstand much higherloads at 45° than the other toothbrushes. Furthermore, the endurance oftooth-brush D was found to increase after a running-in period.

I claim:
 1. A sealing and bearing arrangement in electric toothbrushes(13), said arrangement comprising a cylindrical, rotatable nose pin (1)which has a front member (2) on which a brush (12) is to be mounted, arear member (3) connected to a means (14) transmitting power from amotor (3A), and a central member partly consisting of a thickenedportion (4); and a hollow casing (5) which is immobile when the nose pinrotates and which coaxially encompasses the central member, includingsaid thickened portion (4), and whose front end (7) located proximate tothe front member (2) is open, while its rear end (8) located proximateto the rear member (3) encompasses the nose pin (1), there being aclearance (6) between the inner surface of the casing (5) and thecentral member of the nose pin (1), characterised by a sealing ring (9)for sealing against any unwanted material, said ring being arrangedaround the nose pin (1) in the open end (7) of the casing (5) and beingimmobile when the nose pin (1) rotates; an annular supporting plate (10)which is provided close to and inwardly of the sealing ring (9) towardsthe thickened portion (4) and which is immobile when the nose pin (1)rotates; and bearing balls (11) provided in two races, one on each sideof the thickened portion (4), for taking up forces in all directions,the front race located proximate to the front member (2) being definedby the supporting plate (10), the inner surface of the casing (5), thenose pin (1) and the closest edge of the thickened portion (4), and therear race located proximate to the rear member (3) being defined by therear end (8) of the casing (5), the inner surface of the casing (5), thenose pin (1) and the closest edge of the thickened portion (4). 2.Sealing and bearing arrangement as claimed in claim 1, characterised inthat the sealing ring (9) and the supporting plate (10) are fixed to thefront end (7) of the casing (5) in a press fit.
 3. Sealing and bearingarrangement as claimed in claim 1, characterised in that each raceaccommodates thirteen balls made of hardened steel.
 4. Sealing andbearing arrangement as claimed in claim 1, characterised in that thesealing ring (9) is made of PTFE.
 5. Sealing and bearing arrangement asclaimed in claim 1, characterised in that the nose pin (1), the casing(5) and the supporting plate (10) are made of steel.